Photo-amplifier tube



p 1. K.'SCHLESINGER 2,054,884,

PHOTO-AMPLIFIER TUBE Original Filed Feb. 19, I934 nvc'nfac:

Patented Sept. 22, 1936 UNITED [STATES PATENT OFFICE ary 20, 1933 Divided and this application January 30, 1935, Serial No. 4,058. In Germany Febru- ,2 Claims. (erase-27.5)

The invention relates to photo-electric arrangements for television purposes including a photoelectric tube and an amplifier connected there to, and is a division of my application Serial No.

711,915 filed Feb. 19, 1934.

It is the object of the present invention to combine both arrangements and such as to have a unitary device. The known arrangements of this kind have a relatively high detrimental capacity in the order of more than 5.5 10 mi.

The efiect of the detrimental capacity oi. a photo-tube on the reproduction of the high irequencies is known per se.

It has already been proposed to combine the photo-tube with the amplifier tube to form one capacity of this kind, the ohmic resistance on which the photo-tube acts must be made very small (approximately 5000 ohms in the case of a 180-line image). When using such a small anode resistance, the potentials produced by the 0 photo-tube are not great enough in comparison to the natural noise of the amplifier, so that the production of television images with a large number of lines (for example 180 lines and more) is practically impossible with arrangements of this nature.

The object of the invention is a photo-tube arrangement, the detrimental capacity of which is considerably less than 5.5 10 ml. (for example amounts to approximately 2 cm.), and

which, therefore, permits of the production of television images of the kind in question without special, method).

' According to the invention the photo-tube is arranged in the upper part of an evacuated container and an amplifier stage is arranged in the lower part of this container. A reflector is mounted between said both parts.

The working resistance may, in accordance with complicated means (carrier current the invention, be provided in the tube itself,

and owing to the reduction of the detrimental capacities may be selected to be still larger. The same, for example, with a drop of merely 8% (in a 180-line image) may amount to 20,000-

25,000 ohms. Practically, therefore, as set forth above, a resistance of approximatelytwice'the size, 1. e., up to approximately 50,000 ohms, may be employed, so that the effectiveness of the connection system is nearly ten times greater than that of the previously known arrangements. 1

From these known arrangements that according to the invention difiers fundamentally by the fact that both the capacity of the photo-cathode (which, is practically equal to the radius of the sphere of the tube and, therefore, cannot be made smaller than approximately 2 cm.) as well as the reaction capacity of the amplifier tube do not make a part of the detrimental capacity. and that the remaining grid capacity is substantially smaller than in the case of the known arrangements.

A possible form of embodiment is illustrated in the drawing, in which i is the common vessel, 2 the photo-electric layer provided on the upper part of the wall of the vessel with the lead 4, and 3 a window aperture, through which the light falls onto the photo-electric layer 2. In the lower part of the bulb thereis provided the amplifier system, which comprises the grid 5, the indirectly heated cathode 6, the screening grid 1, the anode 9 and the photo-tube anode resistance Hi. All electrodes may conveniently be secured to a support 9 consisting of insulating material. The end of the grid 5 located in the upper space of the vessel acts as the anode of the photo-tube. At this end there may conveniently be provided a cap II, which contains the metal for the production of the photo-layer 2, or if desired a suitable reaction mixture for developing this metal. In accordance with the invention the diameter of thisc'ap may be made very small.

Naturally it is also possible to mount the cap completely separate from the grid, viz., in such fashion, that it does not form a part of the electrical system.

The cap may be filled, for example, with a mixture of bichromate of caesium and silicon. If the cap is heated to the reaction temperature of the mixture in the manner known per se for example by means of eddy currents, pure metallic caesium is developed, which is deposited in the upper part of the bulb. The part of the bulb intended for the formation of the photo-layer may preferably be furnished with a suitable preliminary coating, for example of metallic silver or silver oxide.

5 In accordance with the invention, there may be provided above the glass support 9 a reflector l2, which is composed for example of metallized mica and does not require to be earthed. This reflector causes in itself reflection or the light and, particularly it the window 0 is provided centrally over the axis 01' the tube, results in a considerably better utilization of the entering light.

It is desirable in accordance with the invention at first to place the amplifier systemin an entirely operable condition (outgassin'g oi the electrodes, atomization of highly emissive metal on Q to the cathode or forming of the oxide cathode), and not until then-in the well evacuated bulbto atomize the metal (for example caesium) serving for the production of the photo-electric layer.

For many purposes of use it is desirable to provide several or all otvthe after-connected amplifler systems 0! the cascade in the same bulb, as in electrodes and said photo-electric layer, said cons,ou,sa4

trol grid projecting through said opening of said screen into said upper part or said container, a small cap containing a reaction mixture. said cap being attached to said projecting end of said grid, and connection means for all of said electrodes, said connection means including supporting means for said anode, cathode and said "his.

2. A photo-amplifier tube comprising an evacuated container provided with a press portion, a photo-electric layer coating the inner wall 01' "the upper part of said container, said coating being provided with a window, a cathode, an anode a control grid and a screening grid in the lower part of said container, a screen provided with an opening mounted between said electrodes and said photo-electric layer, said control grid projecting through said opening of" said screen into said upper part or said container, a small cap containing a reaction mixture, said cap beingattached' to said projecting end of said grid, and connection means for all of said electrodes, said connection means including supporting means for said anode, cathode and said grids, a working resistanceot the order of 50,000

ohms connecting said cathode and said control grid said resistance having low natural capacity.

' KURT SCHLESINGER. 

